Shear Bond Strength of Contemporary CAD/CAM Ceramic Materials to Dentin

Objectives: To compare the shear bond strength and failure mode of two contemporary CAD/CAM ceramic materials to bovine dentin.
Methods: In vitro experimental study. Sixty (60) freshly extracted bovine incisors were randomly distributed into four groups of 15 specimens each. Then, teeth were longitudinal sectioned with a micrometric cutting device, in order to expose dentin. CAD/CAM ceramic discs of Zirconium (Zirconio Biotech, Upcera, Spain) were dried for 30 minutes and sintered while Lithium Disilicate (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein)disks were crystallized. Then, they were bonded to bovine dentin using two different luting materials (RelyX Ultimate, 3M ESPE, United States and Theracem, Bisco, United States) following the surface treatment protocols recommended by manufacturers. Subsequently, shear bond strength tests were performed applying the force at the disc/dentin interface using the universal testing machine (Instron 3366, Instron Corp, United States) at crosshead speed of 0.5 mm/min. Finally, dentin surfaces and ceramic CAD/CAM discs were observed using a stereomicroscope (Stemi® 2000C, Carl Zeiss, Germany) to determine failure mode. Statistical analysis was performed using ANOVA, Tukey, Hsu and Fisher tests.
Results: RelyX Ultimate shear bond strength (SBS) of Lithium Disilicate and Zirconium discs to bovine dentin was significantly higher than the shear bond strength means observed when Theracem was used (p<0.05). No statistically significant differences were observed within groups (Zirconium vs. Lithium Disilicate) at each luting material evaluated. However, SBS in Zirconium groups were always the highest. Failure mode for both luting materials was predominantly adhesive to dentin, independently the CAD/CAM ceramic material evaluated.
Conclusions: Universal luting materials (Relyx Ultimate) generated higher SBS to bovine dentin than Self-adhesive cements (Theracem) for both CAD/CAM ceramic materials evaluated. SBS performance of the luting cements in both restorative materials is similar, when they are evaluated by separate. Bonding to CAD/CAM restorative materials is more predictable, according to the failure mode observed.